Color printing devices, such as, for example, ink-jet printers operate by applying small drops of ink to a print media (e.g., paper), thereby forming dots. Different colored dots are combined to form a variety of desired colors. By way of example, certain ink-jet printers utilize four different colors of ink, namely, cyan, magenta, yellow, and black. These inks are typically supplied by ink printheads having several nozzles, which can be selectively controlled to eject drops of ink onto the print media. The printheads are typically arranged in a printhead carriage that is moveably controlled by a transport mechanism such that a swath of color can be applied to a portion of the print media by selectively controlling the ink printheads moving in relation to the print media.
Certain printing devices are configured to print bi-directionally. This means, for example, that swaths may be printed as the carriage moves across the print media from a right hand side to a left hand side and then back across the paper from the left hand side to the right hand side. This bi-directional movement is then continued on down the print media, as needed to print the desired content.
To reduce the visibility of certain print errors in the resulting print, some printing devices apply selected probabilistic or other like functions in the printing logic to control the usage of nozzles within the printheads. Such probabilistic functions typically print less ink from nozzles near the ends of the printhead. In printing devices such as these, it has been found, however, that for certain colors the bi-directional printing of swaths can lead to the formation of other print errors such as undulating color variations. These variations form unwanted hue shifts that may cause visually noticeable bands in the resulting print.
Consequently, there is a need for improved methods and apparatuses for significantly reducing or eliminating visible hue shift banding in bi-directional color printing devices.
In accordance with certain aspects of the present invention, improved methods and apparatuses are provided for significantly reducing or eliminating visible hue shift banding and/or other like defects produced in bi-directional color printing.
The above stated needs and others are met, for example, by a method for use in printing color swaths in a bi-directional printing device. The bi-directional printing device is configured to use a plurality of color inks including at least one light color ink and at least one dark color ink. The method includes selectively printing at least one dark color ink on a print media based on a non-uniform print mask function. The method further includes selectively printing at least one light color ink on the print media based on a substantially uniform print mask function.
In accordance with still other implementations of the present invention, a printing device that is capable of printing color swaths bi-directionally is provided. Here, the printing device includes a printing mechanism that is controlled by logic. The printing mechanism is configurable to selectively print color swaths on a print media using a plurality of color inks including at least one light color ink and at least one dark color ink. The logic is operatively configured to cause the printing mechanism to selectively print the dark color ink on the print media in a non-uniform probabilistic manner, and selectively print the light color ink on the print media in a substantially uniform probabilistic manner.